1. Field of the Invention
The present invention relates to devices used for controlling the movement of fluids through ducts, conduits, and the like. More particularly, the present invention relates to dampers designed to halt or otherwise divert the flow of fluids, specifically gases, substantially completely. Still more particularly, the present invention relates to louver dampers.
2. Description of the Prior Art
In the field of the control of fluid flow it is important that those mechanical components used to effect the halt of fluid flow do so on demand. In industrial applications where fluids such as by-product and reaction gases move through conduits having dimensions of several feet, the mechanical devices used to affect fluid movement are necessarily sized to such conduits and are therefore quite large. These mechanical devices are generally identified by the term dampers. Some dampers are designed to simply divert fluid flow from one conduit to another, others are designed to block fluid flow completely, while most perform both functions. Under either duty, and with increasing interest in minimizing the amount of untreated or "raw" fluids being exhausted directly to the atmosphere, it is important that the fluid being controlled be substantially prevented from leaking through or around the damper. That is, the damper must provide a 100% gas-tight seal when activated. It is also important to effect such complete isolation so that maintenance personnel may enter the conduit for on-line maintenance downstream of the damper, such as required in the maintenance of scrubbers, precipitators, large fans, and the like. In addition, it is preferable that the sealing or blocking of the conduit be effected as soon as possible.
There are a variety of industrial dampers in use in the field of fluid flow control. There are butterfly dampers, which have one or more flaps that may be actuated to seal or open a port or ports to halt or divert fluids. There are poppet valves that are designed to close off a conduit when seated, and to permit fluid flow in a substantially 90.degree. change of direction. There are guillotine dampers, which act much as a guillotine to cut off fluid flow when actuated to enter the conduit. Finally, there are louver dampers, which act much like Venetian blinds. That is, they are formed of a series of blades that are pivoted about a center axis to be swung into a position parallel to the direction of fluid flow to permit fluid flow through a conduit, and pivoted into a position perpendicular to the direction of fluid flow to halt the flow of fluid through a conduit. More specifically, louver dampers are modulating devices in that they are actuated for balancing of flows, as well as for periodic on-off operation. They also tend to be more compact, and therefore take up less space, at least in comparison to guillotine dampers for example. Each of the noted damper designs has its place, as a function of the size of the conduit, the fluid to be controlled, and the operating conditions, including, but not limited to fluid temperature and flow rates. In most cases, it is important that each of these dampers provides means for ensuring that there is little or no fluid leakage when they are activated to prevent fluid flow in a particular conduit.
As indicated, it is important to use a damper that performs its fluid modulation function and that isolates zones of conduits for maintenance access downstream of the damper. This may be achieved with sophisticated damper systems which are costly and require an extensive amount of space within which to operate, as is the case with guillotine and double-louver dampers. It is to be noted that louver dampers are commonly used in the area of fluid flow through conduits where the goal is to modulate, or stop completely, the fluid flow in the conduit. Initial louver dampers were only used to modulate; later, double-louver dampers were designed to both modulate and isolate.
In some prior uses of louver dampers it has been the practice to ensure that there will be little to no fluid leakage by placing pairs of dampers--or double-louver dampers--throughout the conduit, each of the pair spaced apart from the other of the pair so as to form a gap therebetween. Into this gap a pressurizing purge fluid--usually air that is often pre-heated--is injected. The purging air ensures that no fluid will get from the upstream side of the pair of dampers to the downstream side. Pre-heating of this purge or sealing air prevents condensation of gases and consequent corrosion of the damper's components. Unfortunately, this method involves the use of a sizable amount of purge air and is therefore very costly. It further requires the use of twice as much material to form a pair of louvers rather than a single louver. In addition, while it is possible to use a single actuator to move the paired louvers, there are occasions where each louver damper of the pair has its own actuator. Of course, this too is costly.
More recently, a louver that has been used increasingly in commercial settings has moved the pair of damper blade sets much closer to each other so that a single actuation means is required. U.S. Pat. No. Re. 31,471 to Hagar describes such a louver damper. The Hagar louver damper operates as indicated for louver dampers in general; however, it is formed of a plurality of pairs of blade walls, where each pair of walls is mechanically coupled. The Hagar device is operated such that when the plurality of blades are rotated to block fluid flow, they line up to create a single gap between all of the blade walls. In order to ensure a complete seal so that no fluid will pass through the conduit, the gap is purged with pressurizing air that blocks any leak passageways that may exist. Through this design, a single actuation system is required. The Hagar system is therefore more cost-effective than the previous louver dampers. However, the Hagar design is sensitive to temperature differentials between the upstream and downstream sides of the damper in that thermal expansion of the "hot" side of the damper with respect to the "cold" side causes bowing of the entire damper. This causes bimetallic deflection that can result in a less-than-100% gas-tight seal and mechanical jamming of the components, and is therefore a significant limitation on the applicability of the Hagar double-walled damper where there are temperature variations; particularly so in high-temperature conditions.
U.S. Pat. No. 4,493,342 issued to Bachmann, one of the inventors of the present invention, provides for a more-aerodynamic design of the two blade walls, but it is a double-walled design. It is distinct from the Hagar design in that the two blades or walls are isolated from one another. As a result, bi-metallic deflection is not as significant a concern. Nevertheless, like other double-walled dampers, is more costly than is necessary for the task. These dampers require a considerable amount of material for construction of the double-walled blades of the scale required in many commercial applications. The amount of energy required to actuate such large physical devices in the face of considerable fluid pressures is also substantial. Maintenance of the various components used to form the double-walled louvers is also a concern.
An additional problem in modulating or isolating the flow of a fluid through a conduit has not been satisfactorily addressed in the prior louver designs. It is well known that there are fluids containing solids, sticky substances, and the like, that foul the interior of the conduit. These contaminants tend to build up where the louver interfaces with the interior walls of the conduit. This can prevent the louver from closing completely when required. In order to minimize the effects of this particulate or residue build-up on the operation of the louver, it would be preferable to have a louver designed with a self-cleaning capability.
Therefore, what is needed is a louver damper that is fabricated in a way that minimizes its cost and that is space efficient without compromising its performance in modulating and/or isolating fluids in a conduit. What is also needed is a louver damper that can be operated with a single actuation means. Further, what is needed is a louver damper of sufficiently simple design so as to make operation and maintenance costs minimal. Still further, what is needed is a louver damper designed to ensure no fluid leakage occurs when the louver damper is closed. Additionally, such a louver damper should be designed to minimize effects of thermal stresses. In summary, what is needed is an effective and efficient fluid-flow modulation and/or isolation device that preferably includes self-cleaning capability, particularly when the fluid is contaminated with solids.